Surgical site infections (SSI) account for 37% of US hospital infections and increase morbidity and cost. High rates (10-22%) of SSI are associated with colorectal surgery and obesity. Bacterial resistance requires oxygen, and higher tissue oxygen limits infection in general surgery patients. Control of core and local temperature may increase infection resistance by modulating perfusion, oxygenation, angiogenesis and immune cell responses. Perioperative hypothermia reduces tissue oxygen while normothermia lowers SSI rates. Warming injured tissues locally may offer additional benefit. Increased subcutaneous oxygen (PscO2) and fewer infections are reported in patients receiving pre-surgical local warming. Warming incisions immediately after surgery and intermittently for two days after gastric bypass or colectomy surgery reduced infection rates, but systematic study of clinical outcomes and potential mechanisms is lacking. Further study is needed to determine efficacy and dosage, and to investigate clinical and cellular outcomes. Aim 1: Conduct a large (n=180) randomized clinical trial to more definitively determine the clinical efficacy of local warming (for one hour mmediately post surgery, repeated every 8-10 hours for 5 more sessions) in reducing the incidence of SSI and wound complications. SSI and wound complications will be evaluated during hospitalization and for 6 weeks post-surgery by a) ASEPSIS Wound Scoring System; b) CDC Criteria for Classification of SSI. Aim 2: Compare patients randomized to local warming to those randomized to usual care on a variety of tissue and cellular variables, in order to understand the impact of warming on these variables. Variables to be measured include: 2.1 Wound tissue responses in test wound samples obtained on postoperative day 9, including: a) Indicators of Angiogenesis (determined by flow cytometry): 1. Percent of endothelial progenitor cells (EPC) CD133 positive, CD34 and VEGFR-2 co-expressing) 2. Percent of endothelial cells (CD31 positive) 3. Presence of endothelial cells (CD31 positive) and EPC (CD34 and VEGFR-2 co-expressing) confirmed by mmunohistochemistry. b) Indicators of Immune Response (determined by flow cytometry) 1. Percent of macrophages (CD68 positive), T cells (CDS positive), and B cells (CD20 positive) 2. Presence of macrophages (CD68 positive), T cells (CDS positive), and B cells (CD20 positive) confirmed by Immunohistochemistry c) Indicator of Collagen Synthesis (determined by manual colorimetric microtiter plate assay) 1. Hydroxyproline quantity. 2.2. PscO2 and temperature responses in test wound sites on postoperative days 0, 1 and 2 using a subcutaneous tonometer/micro-electrode and thermocouple system. 2.3. Perfusion (BF) in the surgical incision on postoperative days 3, 5 and 9 using Laser Doppler Flowmetry (LDF).